1. Field of the Invention
This invention relates to an organic film capable of absorbing effectively laser beams, especially semiconductor laser beams of longer wavelengths, and converting the absorbed energy into another kind of energy. More particularly, this invention relates to a novel organic film utilizable as: a photosensitive film in the electrophotographic printing system wherein a semiconductor laser is used as light source; an optical disk recording layer where information can be written in and reproduced from by means of semiconductor laser beams; or an infrared cutting filter.
2. Description of the Prior Art
The electrophotographic printing system wherein a semiconductor laser is used as light source can record desired image information for later reproduction, by modulating the laser with electric signals in response to the image information, and scanning the surface of a photosensitive member with the modulated laser beam by use of a galvano-mirror or the like to form an electrostatic latent image on the photosensitive member, followed by the development with a toner and the successive transfer of the toner image. Lasers for use in this system are generally gas lasers including a helium-cadmium laser (wavelength 441.6 nm) and a helium-neon laser (wavelength 632.8 nm). Accordingly, photosensitive members spectral-sensitized up to a wavelength of 650 nm are adaptable to such light sources. For example, the following types of photosensitive member are known as suitable ones: a type having a photosensitive layer containing a charge-transfer complex of polyvinylcarbazole with trinitrofluorenone; a type provided with a vapor-deposited layer of tellurium sensitized with selenium; a type having two layers, one being a selenium layer vapor-deposited as a charge transport layer on a conductive layer and the other being a selenium-tellurium layer vapor-deposited on the selenium layer; a type having a photosensitive layer of cadmium sulfide spectral-sensitized with sensitizing dye; a type having two separately functioning photosensitive layers of an organic-pigment-containing charge generation layer and a charge transport layer, both spectral-sensitized to longer wavelengths.
On the other hand, the recording film used for the optical disk technique can store high density information in the form of spiral or circular tracks of minute pits (e.g. about 1 .mu.m.phi.) optically detectable. For writing information on such a disk, the surface of its laser-responsive layer is scanned with a converged laser beam, modulated according to the information, thereby forming pits at the positions irradiated with the laser pulses. These pits form a spiral track or circular tracks. The laser-responsive layer can form optically detectable pits by absorption of laser energy. For instance, in a heat mode recording system, the laser-responsive layer absorbs laser energy at the irradiated positions, where minute depressions (pits) are formed through evaporation or fusion by being heated with the absorbed energy. In another heat mode recording system, pits having optically detectable differences in density can be formed with the laser energy absorbed at the irradiated positions.
The information stored in the optical disk can be read by tracing said tracks with a laser beam and detecting an optical difference between the pit and pit-free positions. For instance, the energy of the track-tracing laser beam reflected from the disk is monitored with a photodetector. When the laser beam hits the pit-free position, the output of the photodetector drops. On the contrary, when hitting the pit, the laser beam is sufficiently reflected from an underlying reflecting surface, raising the output of the photodetector.
Recording media hitherto proposed to be used for such an optical disk are principally inorganic materials such as thin metallic film, e.g. vapor-deposited aluminum films and thin films of bismuth, tellurium oxide, and chalcogenite family amorphous glass.
Meanwhile, small-sized and low-cost semiconductor lasers have been developed in recent years. Most of these lasers emit a ray having a wavelength of 750 nm or longer. For recording and/or reproducing information by use of such a semiconductor laser, the laser-responsive film needs to have an absorption maximum in a longer wavelength region (generally from 750 to 850 nm).
However, the existing laser-responsive films, because of the high reflections of laser beams therefrom, have disadvantages in that the utilization efficiency for laser energy is low and a high sensitivity is hence not attainable. Additional disadvantages of these films are that a complicated layer structure is necessary for shifting the spectral sensitivity to a wavelength of 750 nm or longer, and particularly in the case of electrophotographic photosensitive films, the sensitizing dye used will fade out during repeated charging and exposing operations.
Such being the case, there have been proposed organic films highly sensitive to rays of wavelengths of 750 nm and longer. For example, organic films containing the pyrylium dye disclosed in U.S. Pat. No. 4,315,983 or in "Research Disclosure", 20517 (May 1981) and those containing the squarylium dye disclosed in "J. Vac. Sce. Technol." 18(1), pp 105-109, (January/February 1981) are known to be responsive to lasers of wavelengths of 750 nm and longer.
However, no organic film satisfactory in practical use has yet been developed on account of the following difficulties involved: The stability of organic compounds, as a rule, becomes worse with increasing wavelength of the light that they can absorb; that is to say, organic compounds capable of absorbing rays of very long wavelengths are generally liable to be decomposed with a slight temperature rise; The organic film to be used for the electrophotographic printing system or for the optical disk is required at the same time to fulfill various requirements on the performance characteristics.